The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device, which can be preferably used for, for example, a semiconductor device using a nitride semiconductor and a method of manufacturing the device.
In recent years, semiconductor devices using a group III-V compound having a band gap greater than that of Si have attracted attentions. Among them, semiconductor devices using gallium nitride (GaN) having the following advantages is under development: 1) having a great dielectric breakdown field, 2) having a great electron saturation velocity, 3) having a great thermal conductivity, 4) capable of forming a good hetero junction between AlGaN and GaN, and 5) they are non-toxic and highly safe materials.
Further, semiconductor devices which are power MISFETs (metal insulator semiconductor field effect transistors) using gallium nitride and capable of a normally-off operation are under development from the standpoint of its high breakdown voltage and fast switching characteristics.
For example, the following Non-patent Document 1 discloses a MISFET using a hetero junction between AlGaN and GaN and having a structure in which a gate recess is made on the back side relative to the hetero junction in order to achieve a normally-off operation.
The following Non-patent Document 2 discloses a MISFET fabricated by, when making a gate recess on the back side relative to a hetero junction, using an insulating film having a patterned opening as a mask and leaving the insulating film in the device.
The following Non-patent Document 3 includes a description on an effect of reducing the surface potential of AlGaN when a nitride film is used as a surface protective film of an AlGaN/GaN hetero-junction type epi. It discloses, for example, that the surface potential reducing effect is markedly large when the nitride film is formed using Cat-CVD (catalytic chemical vapor deposition.
The following Non-patent Document 4 includes a description on, when various protective films formed by ECR sputtering are used as a surface protective film of an AlGaN/GaN hetero-junction type epi, a surface potential barrier height and an interfacial sheet charge density at the interface between the surface protective film and AlGaN.
The following Patent Document 1 discloses a hetero-junction field effect transistor which is not a transistor with a gate recess but has a field plate layer whose thickness shows a stepwise change.
The following Patent Documents 2 and 3 disclose a semiconductor device which is not a transistor with a gate recess but has a first field plate electrode integrated with a gate electrode and a second field plate electrode integrated with a source electrode.
Patent Documents
[Patent document 1] Japanese Patent No. 4888115
[Patent Document 2] Japanese Patent No. 4417677
[Patent Document 3] U.S. Pat. No. 7,075,125
Non-Patent Documents
[Non-patent Document 1] N. Ikeda et al., “Over 1.7 kV normally-off GaN hybrid MOS-HFETs with a lower on-resistance on a Si substrate”, IE3 International Symposium on Power Semiconductor Devices and ICs (ISPSD), pp. 284-287, 2011.
[Non-patent Document 2] K. Ota et al., “A Normally-off GaN FET with High Threshold Voltage Uniformity Using A Novel Piezo Neutralization Technique”, International Electron Device Meeting (IEDM) 2009, IEDM09-154, 2009.
[Non-patent Document 3] N. Onojima et al., “Reduction in potential barrier height of AlGaN/GaN heterostructures by SiN passivation”, J. Appl. Phys. 101, 043703 (2007).
[Non-patent Document 4] N. Maeda et al., “Systematic Study of Deposition Effect (Si3N4, SiO2, AlN, and Al2O3) on Electrical Properties in AlGaN/GaN Heterostructures”, Jpn. J. Appl. Phys., Vol. 46, No. 2 (2007), pp. 547-554